The measurement steps are shown in Table 1. Zones of the sample and the Bi(III) plating solution were sequentially aspirated into the holding coil (Steps 1 and 2). Then, sample and Bi(III) plating solution were flowed directly to the flow cell while the potential of the electrode was maintained at −1.4V as the preconcentration step (Step 3). After 10 s of equilibration (Step 4), square-wave voltammograms with a frequency of 50 Hz, a step potential of 5 mV, and a pulse amplitude of 50 mV were recorded from −1.4 to 0 V vs. Ag/AgCl (Step 5). Finally, the electrode was cleaned to remove any remaining analyte metals and bismuth film at +0.3 V vs. Ag/AgCl in flowing supporting electrolyte for 30 s (Steps 6 and 7). A measurement cycle for three analytes including Pb(II), Cd(II), and Zn(II) is about 4 min. The electrode was then ready for a new stripping cycle. 1 M hydrochloric acid was used as a supporting electrolyte for all steps. All experiments were performed at room temperature (25 ◦ C) without removing oxygen from the solution.
Measurement procedure